Embodiments of the present invention refer to electrical connectors designed to feed voltage and current to electrical equipment, such as compressor and pump motors, switchgear, subsea VSDs and transformers etc., that is typically installed inside an enclosure, the internal pressure of which is equal to or different than the pressure of the surrounding thereof. In particular, the embodiments refer to a penetrator conducting electric power through a barrier that separates volumes at equal or different pressures.
Electrical connectors are used topside and subsea to conduct electric power to electrical equipment that is installed in controlled environments to avoid the risk of electric discharge and short circuiting. The equipment referred to may be, e.g., voltage or current converters and transformers, motors, power distribution modules etc., operating at supply voltages in the order of 1,000-10,000 V or higher. For the purpose of avoiding electric discharge the electrical equipment may be installed in an enclosure which is filled with gas or liquid that provides the dielectric strength required to prevent formation of electric discharges between structures at different electric potentials. In topside applications the electrical equipment and enclosure are typically maintained at a pressure which is equal to or higher than the pressure prevailing outside the enclosure, and often at a pressure which is considerably higher than the atmospheric pressure at sea level. In subsea applications however, where the electrical equipment and enclosure may be located at depths down to 1,000 m or more, enclosures are typically maintained at a pressure which is equal to or lower than the pressure prevailing outside the enclosure. Thus, the enclosures referred to may in many cases be seen as pressure vessels where the external pressure outside the enclosure can be considerably higher than the internal pressure, or vice versa.
The task of conducting high voltage electric power to the equipment installed in the enclosure raises several problems and challenges. One of them is the task of ensuring a sealed and leak-free passage of a conductor through a wall that separates the internal space and pressure of the enclosure from the pressure of the surroundings thereof. Another challenge is to meet the need for an arrangement that prevents electric discharge between the conductor and nearby mechanical structures at other potential, usually ground potential, where the conductor passes through the wall of the enclosure. In other words, when an energized conductor is near any material at earth potential, it can cause very high electric field strengths resulting in formation of electric discharges.
To this purpose electrical penetrators have been designed for feed-through of a conductor through a wall or partition also acting as barrier between volumes at different pressures. The penetrator enables one or several conductors to pass through the wall or partition of a tank, a vessel or any form of enclosure, and insulates the conductor from the wall or partition. A means of attachment, such as a flange or other fixing device, generally forms a part of the penetrator. Another commonly used name for a penetrator is bushing.
The penetrator is a device or assembly in which a conductor is secured in a termination arrangement that is arranged protected inside a metal case. This metal case is usually an overall cylindrical housing wherein the bare conductor end is secured in an insulator body that is fixated in the housing. A rigid conductor pin is arranged protruding from the insulator body so as to pass through a wall or partition that covers and protects the conductor termination components inside the penetrator housing. The conductor pin extends electrically insulated through an opening in said wall, wherein electrical insulation is provided by means of a tubular insulator body that surrounds the conductor pin. The tubular insulator body is made to fit closely to the periphery of the opening through the wall.
A penetrator housing is typically provided if a cable or other conductor enclosed in an earthed screen is used. The housing then provides a barrier so that the inside of the housing can be filled with a dielectric fluid. Also, the housing provides earth connection between the (cable) screen and the penetrator wall.
In a forward end of the penetrator housing, if appropriate, the housing may be formed externally with a radially projecting flange that carries attachment means, such as bolt holes for bolts or similar, by which the penetrator can be mounted to the enclosure. Said flange can also be an integrated circumferential portion of the wall. A sealing ring is typically arranged to be clamped between the flange on the penetrator housing and a corresponding flange arranged on the enclosure that houses the electrical equipment.
As the penetrator assembly is mounted to the enclosure, said wall or partition acts as physical barrier between the volume of gas or liquid that occupies the internal space of the enclosure and a volume of gas or liquid that occupies the internal space of the penetrator. The internal volumes of the enclosure and penetrator can be at equal pressure, but are more usually set under different pressures. One or both volumes can be provided pressure compensation means for adjustment of internal pressure with regard to the pressure in a surrounding media, such as seawater. Since at 1,000 m below sea level, e.g., the pressure outside the penetrator and the enclosure is about 100 bar it is readily understood that the wall and the feed-through of the conductor requires proper attention in terms of design and performance.